To convert a color of an image that is photographed under a light source different from an observation light source into a color equivalent to a color of an image that is photographed under the observation light source, color correction processing is required, in which color data under a photography light source is converted into color data under the observation light source.
Patent Literature 1 describes a method for calculating a color correction condition for color space conversion although the method does not correct the difference between the light sources. Patent Literature 1 provides a color conversion matrix by a least-square method. The color conversion matrix causes RGB signal values obtained by photographing a color chart to match with target RGB signal values obtained from colorimetric values of the color chart.